1. Field of the Invention
The invention relates to a self-priming centrifugal pump for conveying a liquid medium including
a pump housing which has a suction passage and a discharge passage,
a pump chamber which is provided in the pump housing and has an inlet and an outlet,
a pump impeller which is arranged in the pump chamber and which has a suction opening opposed to the inlet of the pump chamber,
a working fluid chamber which is provided in the pump housing and which is connected to the outlet of the pump chamber and to the discharge passage in the pump housing,
a jet pump diffuser which has a broadened outlet, in which a reduced pressure is produced, and a constricted inlet, the outlet of the diffuser being connected to the inlet of the pump chamber whilst the inlet of diffuser is in communication with the suction passage in the pump housing and
a jet pump drive nozzle which has an inlet and an outlet, the inlet of the drive nozzle being connected to a supply passage connected to the working fluid chamber whilst the outlet of the drive nozzle within the suction passage cooperates in the manner of an injector with the inlet of the diffuser.
2. Prior Art
It is known in connection with centrifugal pumps to provide a venturi nozzle or jet pump device upstream of the pump impeller in order to produce self-priming of the liquid medium to be conveyed even when there is air in a suction passage leading upwards to the rotary pump. The diffuser tube of the jet pump device, into whose inlet the jet pump drive nozzle discharges, constitutes the sole connection between the suction passage in the pump housing and the suction opening of the pump impeller in the known self-priming centrifugal pumps of the type referred to above. When the centrifugal pump is switched on, a liquid working medium, which remains in the working medium chamber of the pump housing when the pump is switched off, is firstly pumped by the pump impeller in a circuit from the working medium space through the drive nozzle in the manner of an injector into the diffuser tube, sucked out of the diffuser tube and transferred back into the working medium space again. The working medium jet entering the diffuser tube from the drive nozzle entrains air from the suction passage in the pump housing. The air can then escape from the working medium space, for instance through the discharge passage in the pump housing which is in communication with the working fluid space. When the transfer medium drawn into the suction passage by the reduced air pressure has completely filled the suction passage and is drawn in through the diffuser tube by the pump impeller, the rotary pump builds up its ultimate discharge pressure by which the transfer medium is forced out of the discharge passage of the pump housing connected to the working medium space.
In the aforementioned known self-priming centrifugal pumps the suction efficiency and discharge performance are principally determined by the dimensioning of the drive nozzle and of the diffuser. In order to achieve the jet pump action necessary for the air intake, the diffuser inlet cooperating in the manner of an injector with the drive nozzle necessarily has a small cross-section for the transfer medium which is sucked in, whereby relatively small pumped flows are produced at full output of the rotary pump and also high flow velocities within the centrifugal pump which lead to efficiency losses. In order to change the suction efficiency of the jet pump device for the air intake and to change the suction and discharge capacity of the pump for conveying transfer medium which has been sucked in, the drive nozzle must be able to be changed or adjusted with expensive features and means.